1. Field of the Invention
The present invention relates to a semiconductor device manufacturing method and, more particularly, a semiconductor device manufacturing method including a step of ashing resist employed as a mask upon patterning a metal film.
2. Description of the Prior Art
In the case of forming wirings of a semiconductor devices, a metal film is formed as wirings by etching anisotropically a metal film which is not covered with a resist, for example, after a resist pattern is formed on the metal film including aluminum as a principal component, i.e. the aluminum-based metal film. In this etching, a gas including halogen atoms like chlorine is in general employed.
After conductive patterns are formed, the resist formed on the conductive patterns have been removed by ashing, then surfaces of the conductive patterns and their peripheral area have been processed by wet process using water or chemicals such as acid, alkali. In many cases, the gas employed in the ashing step is made of a gas which is formed by adding the water (H.sub.2 O), carbon tetrafluoride (CF.sub.4), or the like to oxygen (O.sub.2) as a principal component.
In the meanwhile, it has already been known that, if the metal film including aluminum as a principal component is dry-etched anisotropically with the use of a chlorine containing gas, chlorine atoms still remain on the surface of the metal film and its peripheral underlying surface.
Therefore, if the wafer on which the wirings are formed is taken out into the air, chlorine atoms react with moisture in the atmosphere to thus generate hydrochloric acid on the wafer. The hydrochloric acid reacts with aluminum constituting the wirings to thus cause corrosion of the wirings. This corrosion causes reduction in reliability of the semiconductor device and degradation in yielding.
In order to prevent generation of the corrosion of the wirings, various approaches have been tried until now. Several examples of such approaches will be explained herein below.
In Patent Application Publications (KOKAIs) 3-138122 and 2-80585, it has been proposed that contact between chlorine and the air can be prevented if a film such as a polymer film is formed on the surface of the wafer after the etching step or ashing step and the wafer is then taken out into the air. However, according to this approach, the etching apparatus must be equipped with a film depositing apparatus and therefore a manufacturing cost of the etching apparatus enormously goes up. In addition, maintenance process of the film deposition apparatus, e.g., cleaning process to remove trash, is needed. Besides, since the film such as the polymer film must be removed prior to succeeding steps, much time and labor are required.
In Patent Application Publication (KOKAI) 2-165656, another approach has been set forth wherein, after the etching step and the ashing step are carried out, an interlayer film such as an SiO.sub.2 film can be deposited by the same apparatus without taking out the wafer into the air. This approach is effective in that regions on the wafer to which chlorine atoms are stucked are not exposed to the air. But this approach has such problems that chlorine atoms serving as the cause of corrosion still remain on the wafer and that etching residue cannot be removed by the wet process. In addition, since the interlayer film depositing apparatus must be provided to the etching apparatus, a manufacturing cost of the etching apparatus also extremely goes up.
In Patent Application Publications (KOKAIs) 3-166724 and 3-180040, another approach has been proposed wherein, after the etching step or ashing step is carried out, the wafer can be post-processed by the wet process with the use of water, organic solvent, or the like. Although the wet process is capable of having a considerable effect on removal of chlorine, exposure of the wafer to the air cannot be avoided. It may of course be considered that the wet process is conducted under vacuum, but such technique is not practical since a manufacturing cost of the apparatus would be increased extremely higher.
In addition, in Patent Application Publications (KOKAIs) 57-89477 and 4-64233, another approach has been set forth wherein, after the etching step or ashing step is carried out and before the wafer is taken out from the apparatus, a laser beam is irradiated to the wafer in the vacuum atmosphere, otherwise the wafer is heated in the vacuum atmosphere to thus remove chlorine from the wafer. However, this approach has such disadvantages that, since a laser device must be mounted on the etching apparatus or the ashing apparatus, otherwise another stage or another chamber on or in which the laser device is mounted must be provided, the apparatus becomes complicated in structure and a manufacturing cost of the apparatus is also increased higher.
On the contrary, as the chlorine removing approach which does not render the etching apparatus or the ashing apparatus complicated in structure and higher in cost, following approaches have been proposed.
In Patent Application Publications (KOKAIs) 4-259220 and 7-254589, an approach has been proposed wherein, upon ashing the resist, a step of removing chlorine from the wafer can be carried out simultaneously with the ashing step by use of a gas mixture of oxygen, methanol, and isopropyl alcohol.
Further, in Patent Application Publication 3-41728, another approach has been set forth wherein, after the ashing step is carried out by use of CF.sub.4 and O.sub.2, the H.sub.2 O gas is supplied to the wafer without plasmanization to remove chlorine on the wafer. However, it has been reported by a literature, "Kondo et al., Proceeding of 13th Symposium on Dry Process, 10. 24, 1991" that chlorine cannot be completely removed according to this approach.
In addition, in Kondo's literature and Japanese Pat. No. 2,510,053, it has been set forth that corrosion generation can be prevented by the down-flow ashing employing O.sub.2 and H.sub.2 O. This approach is capable of achieving a significant effect on the removal of chlorine atoms from the wafer. However, in Kondo's literature and Japenese Pat. No. 2,510,053, it has not been mentioned what influence is exerted on the prevention of the corrosion generation according to an amount of H.sub.2 O gas added during the down-flow ashing employing O.sub.2 and H.sub.2 O. Further, it has not mentioned what influence is caused on prevention of the corrosion generation and generation of the ashing residue by a combination of the down-flow ashing employing O.sub.2 and H.sub.2 O and the wafer heating temperature.
The O.sub.2 /H.sub.2 O down-flow ashing has also been set forth in Patent Application Publication (KOKAI) 6-333924. It has been disclosed in this Patent Application Publication (KOKAI) 6-333924 that, if ultra violet (UV) cure is effected before the etching step, a deteriorated layer which is formed on the surface of the resist during the etching step does not remain as the etching residue on the wafer after the O.sub.2 /H.sub.2 O down-flow ashing is completed. The deteriorated layer is formed because chlorine included in the etching gas and etched aluminum atoms are stuck respectively to the surface of the resist and than such chlorine and aluminum atoms react with the resist according to the wafer heating temperature. Unless such UV cure is effected, the deteriorated layer easily remains as the etching residue.
However, chlorine serving as the cause of corrosion is not only included in the resist residue, but also absorbed by the side wall portions of the patterned aluminum wirings, for example. Therefore, an effect of preventing the corrosion generation can be insufficiently achieved by merely preventing the generation of the resist residue. In addition, although the removal of the deteriorated layer by virtue of the UV cure has the effect of removing the chlorine, the apparatus becomes complicated in structure since a UV irradiating means has to be provided to the apparatus.